/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.tags.form;

import java.beans.PropertyEditor;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

import org.springframework.util.CollectionUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.web.servlet.support.BindStatus;

/**
 * Utility class for testing whether a candidate value matches a {@link BindStatus#getValue data bound value}.
 * Eagerly attempts to prove a comparison through a number of avenues to deal with issues such as instance
 * inequality, logical (String-representation-based) equality and {@link PropertyEditor}-based comparison.
 *
 * <p>Full support is provided for comparing arrays, {@link Collection Collections} and {@link Map Maps}.
 *
 * <p><h1><a name="equality-contract">Equality Contract</a></h1>
 * For single-valued objects equality is first tested using standard {@link Object#equals Java equality}. As
 * such, user code should endeavour to implement {@link Object#equals} to speed up the comparison process. If
 * {@link Object#equals} returns {@code false} then an attempt is made at an
 * {@link #exhaustiveCompare exhaustive comparison} with the aim being to <strong>prove</strong> equality rather
 * than disprove it.
 *
 * <p>Next, an attempt is made to compare the {@code String} representations of both the candidate and bound
 * values. This may result in {@code true} in a number of cases due to the fact both values will be represented
 * as {@code Strings} when shown to the user.
 *
 * <p>Next, if the candidate value is a {@code String}, an attempt is made to compare the bound value to
 * result of applying the corresponding {@link PropertyEditor} to the candidate. This comparison may be
 * executed twice, once against the direct {@code String} instances, and then against the {@code String}
 * representations if the first comparison results in {@code false}.
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 2.0
 */
abstract class SelectedValueComparator {

    /**
     * Returns {@code true} if the supplied candidate value is equal to the value bound to
     * the supplied {@link BindStatus}. Equality in this case differs from standard Java equality and
     * is described in more detail <a href="#equality-contract">here</a>.
     */
    public static boolean isSelected(BindStatus bindStatus, Object candidateValue) {
        if (bindStatus == null) {
            return (candidateValue == null);
        }

        // Check obvious equality matches with the candidate first,
        // both with the rendered value and with the original value.
        Object boundValue = bindStatus.getValue();
        if (ObjectUtils.nullSafeEquals(boundValue, candidateValue)) {
            return true;
        }
        Object actualValue = bindStatus.getActualValue();
        if (actualValue != null && actualValue != boundValue &&
                ObjectUtils.nullSafeEquals(actualValue, candidateValue)) {
            return true;
        }
        if (actualValue != null) {
            boundValue = actualValue;
        } else if (boundValue == null) {
            return false;
        }

        // Non-null value but no obvious equality with the candidate value:
        // go into more exhaustive comparisons.
        boolean selected = false;
        if (boundValue.getClass().isArray()) {
            selected = collectionCompare(CollectionUtils.arrayToList(boundValue), candidateValue, bindStatus);
        } else if (boundValue instanceof Collection) {
            selected = collectionCompare((Collection<?>) boundValue, candidateValue, bindStatus);
        } else if (boundValue instanceof Map) {
            selected = mapCompare((Map<?, ?>) boundValue, candidateValue, bindStatus);
        }
        if (!selected) {
            selected = exhaustiveCompare(boundValue, candidateValue, bindStatus.getEditor(), null);
        }
        return selected;
    }

    private static boolean collectionCompare(Collection<?> boundCollection, Object candidateValue,
            BindStatus bindStatus) {
        try {
            if (boundCollection.contains(candidateValue)) {
                return true;
            }
        } catch (ClassCastException ex) {
            // Probably from a TreeSet - ignore.
        }
        return exhaustiveCollectionCompare(boundCollection, candidateValue, bindStatus);
    }

    private static boolean mapCompare(Map<?, ?> boundMap, Object candidateValue, BindStatus bindStatus) {
        try {
            if (boundMap.containsKey(candidateValue)) {
                return true;
            }
        } catch (ClassCastException ex) {
            // Probably from a TreeMap - ignore.
        }
        return exhaustiveCollectionCompare(boundMap.keySet(), candidateValue, bindStatus);
    }

    private static boolean exhaustiveCollectionCompare(
            Collection<?> collection, Object candidateValue, BindStatus bindStatus) {

        Map<PropertyEditor, Object> convertedValueCache = new HashMap<>(1);
        PropertyEditor editor = null;
        boolean candidateIsString = (candidateValue instanceof String);
        if (!candidateIsString) {
            editor = bindStatus.findEditor(candidateValue.getClass());
        }
        for (Object element : collection) {
            if (editor == null && element != null && candidateIsString) {
                editor = bindStatus.findEditor(element.getClass());
            }
            if (exhaustiveCompare(element, candidateValue, editor, convertedValueCache)) {
                return true;
            }
        }
        return false;
    }

    private static boolean exhaustiveCompare(Object boundValue, Object candidate,
            PropertyEditor editor, Map<PropertyEditor, Object> convertedValueCache) {

        String candidateDisplayString = ValueFormatter.getDisplayString(candidate, editor, false);
        if (boundValue != null && boundValue.getClass().isEnum()) {
            Enum<?> boundEnum = (Enum<?>) boundValue;
            String enumCodeAsString = ObjectUtils.getDisplayString(boundEnum.name());
            if (enumCodeAsString.equals(candidateDisplayString)) {
                return true;
            }
            String enumLabelAsString = ObjectUtils.getDisplayString(boundEnum.toString());
            if (enumLabelAsString.equals(candidateDisplayString)) {
                return true;
            }
        } else if (ObjectUtils.getDisplayString(boundValue).equals(candidateDisplayString)) {
            return true;
        }

        if (editor != null && candidate instanceof String) {
            // Try PE-based comparison (PE should *not* be allowed to escape creating thread)
            String candidateAsString = (String) candidate;
            Object candidateAsValue;
            if (convertedValueCache != null && convertedValueCache.containsKey(editor)) {
                candidateAsValue = convertedValueCache.get(editor);
            } else {
                editor.setAsText(candidateAsString);
                candidateAsValue = editor.getValue();
                if (convertedValueCache != null) {
                    convertedValueCache.put(editor, candidateAsValue);
                }
            }
            if (ObjectUtils.nullSafeEquals(boundValue, candidateAsValue)) {
                return true;
            }
        }
        return false;
    }

}
